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 ###Instrução: Qual é o número de medalhas de bronze para o Canadá e a prata é menor que 0?
 ###Tabelas: CREATE TABLE parliaments_of_king_edward_iv (parliaments_of_king_edward_iv_id AUTO_INCREMENT PRIMARY KEY, Summoned VARCHAR, Elected VARCHAR, Assembled VARCHAR, Dissolved VARCHAR, 1st member VARCHAR, 2nd member VARCHAR) CREATE TABLE list_of_sponsored_cosponsored_legislation (list_of_sponsored_cosponsored_legislation_id AUTO_INCREMENT PRIMARY KEY, Years covered VARCHAR, All bills sponsored INT, All amendments sponsored INT, All bills cosponsored INT, All amendments cosponsored INT, Original bills cosponsored INT, Original amendments cosponsored INT, Bill support withdrawn INT, Amendment support withdrawn INT) CREATE TABLE building_and_withdrawal_data (building_and_withdrawal_data_id AUTO_INCREMENT PRIMARY KEY, Number INT, Builder VARCHAR, Built VARCHAR, Rebuilt VARCHAR, Name as rebuilt VARCHAR, Scrapped/Sold VARCHAR) CREATE TABLE teen_edition_housemates (teen_edition_housemates_id AUTO_INCREMENT PRIMARY KEY, Name VARCHAR, Home or representative town or province VARCHAR, Age INT, Edition VARCHAR, Total days in PBB House INT, Duration VARCHAR, Status VARCHAR) CREATE TABLE medal_table (medal_table_id AUTO_INCREMENT PRIMARY KEY, Rank INT, Nation VARCHAR, Gold INT, Silver INT, Bronze INT, Total INT)  
SELECT SUM Bronze FROM medal_table WHERE Nation = canada AND Silver < 0